At least three people were shot dead during anti-government protests in Caracas, escalating the worst bout of unrest in Venezuela since turmoil after President Nicolas Maduro's election last year.

The violence was a crescendo to weeks of sporadic demonstrations in the provinces led by opposition hardliners who denounce Maduro for failing to control inflation, crime and product shortages and vow to push him from office.

The government says the opposition is sowing violence to stage a coup similar to the one a decade ago that briefly ousted late socialist leader Hugo Chavez, though there are few signs that the current melees could topple Maduro.

The country's top prosecutor confirmed the death of a student and a pro-government community leader amid chaotic scenes as marches by opposition and government sympathizers ended just a few blocks apart in the city centre.

Maduro said another student suffered serious brain damage and was in critical condition after being shot in the head.

"This violent group had failed until now in their attempts to fill Venezuela with death and blood," Maduro said in a speech outside Caracas to commemorate an independence-era battle.

"Today we lament the death of two young Venezuelans."

Reuters reporters on the scene heard gunshots and saw one man carried away dead with blood gushing from his head.

Twenty-three people were injured, 25 arrested, four police vehicles burnt, and some government offices vandalized in violence throughout the day, officials said.

The mayor of stridently opposition municipality of Chacao, in the east of the city, said on Twitter that a third person had been shot dead in his district.

Social networks quickly fell into a familiar pattern of recriminations, with both sides blaming the other based on little clear information about what had happened.

Opposition activists said armed government supporters belonging to hardline groups known as "colectivos" had fired on the peaceful march. Government officials pinned the deaths on "fascists" who they said had planned violence from the start.

"THE EXIT"

As night fell, soldiers fired tear gas at several hundred young demonstrators who burned tires and blocked the main avenue of Chacao, where the third death occurred.

"We're staying in the streets until this government falls," said student Jose Jimenez, 22, protesting in Chacao with a shirt tied round his face to protect him from tear gas.

In 2002, opposition leaders began what would become years of constant protests as part of failed efforts to oust the late Chavez, which included a bungled coup, a two-month oil industry shutdown and an unsuccessful recall referendum.

"They cannot take us back to the scenes of 2002," Maduro said during a speech before the shooting broke out.

Sporadic political protests of varying intensity have been common over the last decade, but they frequently fizzle out within several days as citizens grow weary of blocked streets and the smell of burning debris.

Hardline opposition leader Leopoldo Lopez, a photogenic US-educated former mayor, has led a renewed wave of demonstrations over the last two weeks under the banner "The Exit," in reference to Maduro's departure.

He is seeking to tap into the frustration of Maduro's critics who say state institutions including courts and the electoral council are so controlled by the ruling Socialist Party as to make democracy impossible.

"This movement of people in the streets is going to grow. It's like a wave that will keep growing," Lopez told a Colombian television station.

OPPOSITION UNITY COLLAPSES

The opposition rallied around state governor Henrique Capriles last year after he staged a better-than-expected showing against Maduro in the April election to replace Chavez, but has since stepped out of the limelight to focus on local issues.

Wednesday's violence may formally mark a widening rift between hardliners and those who favor returning to bread-and-butter issues such as sporadic trash collection, filthy streets and pot-holed highways.

Opposition moderates note that their biggest successes, such as turning pro-Chavez strongholds into opposition territory, resulted from leaders stepping away from theatrical street protests to focus on voters' concerns.

The constant protests have also helped the government cement an image of the opposition as saboteurs. Many are wary of being cast in that light again.

"While there are plenty of reasons to protest, there does not seem to be an agenda for the current wave. #LaSalida (The Exit) is not a strategy. It's a hashtag!" complained the anti-government blog Caracas Chronicles.

"The street protests, along with the public bickering they are engendering, are creating a false sense that our actions can undo the regime."